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Exploratory Synthetic Studies of the Praseodymium/Di-2-Pyridyl Ketoxime System Leads to Unusual Reactivity and
Christina Stamou1, Christina Polyzou1, Constantinos C Stoumpos1
1Department of Chemistry, University of Patras, 26504 Patras, Greece.
Abstract:
Reactions of lanthanoid(III) ions with di-2-pyridyl ketoxime, dpkoxH, have been studied. Full synthetic investigation of the Pr(NO3)3·6H2O/dpkoxH reaction system has provided access to complexes [Pr2III(NO3)4(L)2] (isolated as MeCN and MeNO2 solvates; 1 and 2), [Pr4III(OH)2(NO3)4(dpkox)6(EtOH)2] (3) and [Pr8IIIPrIVO4(OH)4(NO3)4(dpkox)12(H2O)4] (4). A novel PrIII-assisted/promoted ligand transformation has occurred in the dinuclear complexes, where L- is the anion of di(pyridin-2-yl)methanone O-(1-hydroxy-1,1-di(pyridin-2-yl)) methyl oxime (HL). Mechanistic schemes have been proposed. In 1 and 2, the two PrIII centers are bridged by two deprotonated oxygen atoms of two "head-to-head" 2.2011110 (Harris notation) L- ligands. The tetranuclear molecule 3 is held together by two μ3-hydroxido groups, two 2.2110, two 2.1110 and two 3.2110 dpkox- ligands. The {Pr4III(μ3-OH)2}10+ unit of the {Pr4III(μ3-OH)2(μ2-oximato)4}6+ core comprises four coplanar PrIII ions in a "butterfly"-type disposition. In the highly symmetrical cluster 4, the nine Pr ions are held together by four μ3-O2- and four μ3-OH- groups, as well as four 2.1110, four 3.2111 and four 2.2110 dpkox- ligands. The inorganic {Pr8IIIPrIV(μ3-O)4(μ3-OH)4}16+ unit of the core can be described as four fused "butterflies", the PrIV center being the common site at one of their "body" positions. The X-band (∼9.5 GHz) EPR spectrum of 4 at 4.2 K shows a sharp peak at 630 G, a derivative feature at 1340 G, and a multitude of weaker signals; the data are compatible with the presence of the half-integer spin expected for the 4f1 PrIV center.
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